The present invention relates to an equalizer arrangement for a digital signal receiving system, and, more particularly, to such an arrangement having a compromise equalizer that implements a prescribed transfer function.
Circuit arrangements of this type are already generally known (see e.g., NTG Technical Reports 88, "Approaches to the Integrated Communication Network," pages 50 to 57), for the purpose of equalizing digital signals that have been transmitted by means of an analog transmission process and have therefore been subjected to distortion both by precursors of the subsequent digital signals and by precursors of received digital signals. In particular, strong linear distortions occur in the digital subscriber lines of the (ISDN) Integrated Services Digital Network, which must be eliminated by appropriate regeneration methods in the digital signal receiving equipment. The distortions caused by precursors are generally minor. For example, a transversal filter with two to four filter coefficients is sufficient for equalization. On the other hand, distortions that are caused by postcursors are very large. They can be compensated, for example, by a equalizer connected upstream of the decision feedback equalizer. The number of regenerator coefficients in this case lies between 20 and 40. However, in the case of digital signals with higher values, such as those coded according to a 2B1Q line code, convergence and stability problems may occur in equalizers of this kind when distortions are severe.